X-ray imaging is often used to obtain images of internal organs of human or animals. Imaging of blood vessels by x-rays, also called angiography, is routinely performed in clinics to detect artery thrombosis or coronary artery diseases. Clinical angiography requires injecting a contrast agent that has a high x-ray absorption coefficient. The contrast agent includes elements having high atomic numbers, such as iodine. Due to the similarity of the absorption capability between blood, serum, vessels and neighboring tissues, it is difficult to produce recognizable contrast in the radiographs without using contrast agents. Injection of the contrast agents partially replaces the blood in the blood vessel with an x-ray absorbing fluid to create contrast in the x-ray images. The vessels appear darker than surrounding tissues if positive film is used, and brighter if negative film is used.
The materials in the contrast agents that enhance x-ray absorption are generally harmful to the human body, and the injection procedure is often painful and dangerous. Passing absorption contrast agents through body vessels can cause both adverse long and short term side effects to the patient. If not administered safely, the injection process can cause serious injury or even fatality.